I come from the net

BeelzeKnightmon - Knightmon's helmet is fused with Beelzemon's mask resulting in the top of the helmet resembling Beelzemon's mask while retaining Knightmon's bevor. The rest of the armor resembles a mix of Beelzemon and RhodoKnightmon's armor with a cape on the back.

Wields a held weapons that converts between a giant sword and a cannon.

And since you started with Beelzemon, let's try his love interest next:
Calmaramon x Mervamon = ?

Junior Commander

Mervamon Black Course Sword - The ultimate incarnation of beauty (apparantly). This "summer" version of Mervamon was born from a gatcha game that awarded costume changes in the summer. Mervamon gains a sea shell themed outfit, and her sword takes the shape of a massive squid. The sword's tentacles are used to restrain the foe before attacking with a giant, inky slash (Black Course Sword).

I come from the net

Alternatively, Mervamon Scylla Mode - Mervamon gets Calmaramon's left forearm & hand. Her lower body is also Calmaramon's but the distal tentacular clubs have been transformed into a pair of Medullia while the mantle now resembles the body of a lamprey.